Synthesis, structure, and magnetic properties of extended 2-D triangular lattices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.Includes bibliographical references.A series of pure iron jarosites (formula AFe₃(OH)₆(TO₄)₂) possessing the paradigmatic kagomé lattice has been prepared stoichiometrically pure through the use of a redox-based hydlrothermal synthetic strategy. This synthetic method allows us grow single crystals from which we fully characterize the structure and magnetic properties. Iron jarosites show signature spin frustrated behavior, indicated by a large Curie-Weiss constant, [theta] [approx.] -800 K, with a transition temperature, ... narrowly ranging from 56 - 65 K. Long-range antiferromagnetic order is due to a canted spin structure developed from the Dzyaloshinsky-Moriya (DM) interaction. Although the DM interaction energy is only 1.2 cm⁻¹, this is large enough to give rise to a 3-D magnetic structure, precluding the ability to study the ground state physics of a purely 2-D frustrated spin system. Copper hydroxy-bridged triangular species have been prepared and characterized both structurally and magnetically. Overall, the nearest-neighbor exchange interaction is found to be antiferromagnetic in each compound, with [Theta] ranging from -18 to -300 K, although the 1-D material lindgrenite, Cu₃(OH)₂)(MoO₄)₂, and the kagomé-lattice-containing material clinoatacamite, Cu₂(OH)₃Cl, show 3-D long-range ferromagnetic order. The compound zinc paratacamite presents the hallmark of an S = 1/2 Cu²⁺ compound possessing the kagomé lattice. This compound has magnetically isolated layers, and we find no evidence for magnetic ordering to temperatures down to 2 K, despite strong nearest-neighbor antiferromagnetic coupling, indicated by [Theta] [approx.] -300 K.by Bart M. Bartlett.Ph.D

Nitrate Radical Facilitates Indirect Benzyl Alcohol Oxidation on Bismuth(III) Vanadate Photoelectrodes

Bismuth(III) vanadate (BiVO4) films show activity for direct benzyl alcohol (PhCH2OH) oxidation to benzaldehyde (PhCHO) in acetonitrile solvent. Introducing tetrabutylammonium nitrate (Bu4NNO3) drastically reduces the overpotential required to generate the PhCHO product while maintaining a high faradaic efficiency (FE) >90 %. BiVO4 corrosion accompanies PhCH2OH oxidation. However, the presence of nitrate ions (NO3−) results in significantly less bismuth‐ and vanadium‐ion leaching (determined by ICP‐MS analysis), as well as reduced surface roughening (determined by SEM imaging). In this reaction, it is proposed that rate‐determining NO3− oxidation generates a highly reactive nitrate radical (NO3⋅) that reacts with PhCH2OH by hydrogen‐atom abstraction (HAT). NO3− is stoichiometrically consumed by the irreversible formation of electrochemically inert HNO3, characterized by an ECi mechanism, rather than a catalytic EC′ mechanism. In the presence of PhCH2OH, NO3− oxidation on BiVO4 becomes more facile; every order of magnitude increase in PhCH2OH concentration shifts the NO3−/ NO3⋅ equilibrium potential negatively by 200 mV. The shift results from the introduction of a consumption pathway for the nitrate radical intermediate via a coupled chemical step with benzyl alcohol. This report is the first example of photoelectrochemical NO3⋅ generation to initiate indirect PhCH2OH oxidation.Initiate to generate: Bismuth(III) vanadate (BiVO4) films show activity for direct benzyl alcohol (PhCH2OH) oxidation to benzaldehyde (PhCHO) in acetonitrile solvent. Introducing tetrabutylammonium nitrate (Bu4NNO3) drastically reduces the overpotential required to generate the PhCHO product while maintaining a high faradaic efficiency. BiVO4 corrosion accompanies PhCH2OH oxidation. Moreover, the presence of nitrate ions (NO3−) results in significantly less bismuth‐ and vanadium‐ion leaching as well as reduced surface roughening.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162788/3/celc202000911.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162788/2/celc202000911-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162788/1/celc202000911_am.pd

Hybrid differentiation strategies for simulation and analysis of applications in C

Computationally efficient and accurate derivatives are important to the success of many different types of numerical methods. Automatic differentation (AD) approaches compute truncation-free derivatives and can be efficient in many cases. Although present AD tools can provide a convenient implementation mechanism, the computational efficiency rarely compares to analytically derived versions that have been carefully implemented. The focus of this work is to combine the strength of these methods into a hybrid strategy that attempts to achieve an optimal balance of implementation and computational efficiency by selecting the appropriate components of the target algorithms for AD and analytical derivation. Although several AD approaches can be considered, our focus is on the use of template overloading forward AD tools in C++ applications. We demonstrate this hybrid strategy for a system of partial differential equations in gas dynamics. These methods apply however to other systems of differentiable equations, including DAEs and ODEs

Bioinformatics : indispensable, yet hidden in plain sight?

BACKGROUND: Bioinformatics has multitudinous identities, organisational alignments and disciplinary links. This variety allows bioinformaticians and bioinformatic work to contribute to much (if not most) of life science research in profound ways. The multitude of bioinformatic work also translates into a multitude of credit-distribution arrangements, apparently dismissing that work. RESULTS: We report on the epistemic and social arrangements that characterise the relationship between bioinformatics and life science. We describe, in sociological terms, the character, power and future of bioinformatic work. The character of bioinformatic work is such that its cultural, institutional and technical structures allow for it to be black-boxed easily. The result is that bioinformatic expertise and contributions travel easily and quickly, yet remain largely uncredited. The power of bioinformatic work is shaped by its dependency on life science work, which combined with the black-boxed character of bioinformatic expertise further contributes to situating bioinformatics on the periphery of the life sciences. Finally, the imagined futures of bioinformatic work suggest that bioinformatics will become ever more indispensable without necessarily becoming more visible, forcing bioinformaticians into difficult professional and career choices. CONCLUSIONS: Bioinformatic expertise and labour is epistemically central but often institutionally peripheral. In part, this is a result of the ways in which the character, power distribution and potential futures of bioinformatics are constituted. However, alternative paths can be imagined

Hidden in the Middle : Culture, Value and Reward in Bioinformatics

Bioinformatics - the so-called shotgun marriage between biology and computer science - is an interdiscipline. Despite interdisciplinarity being seen as a virtue, for having the capacity to solve complex problems and foster innovation, it has the potential to place projects and people in anomalous categories. For example, valorised 'outputs' in academia are often defined and rewarded by discipline. Bioinformatics, as an interdisciplinary bricolage, incorporates experts from various disciplinary cultures with their own distinct ways of working. Perceived problems of interdisciplinarity include difficulties of making explicit knowledge that is practical, theoretical, or cognitive. But successful interdisciplinary research also depends on an understanding of disciplinary cultures and value systems, often only tacitly understood by members of the communities in question. In bioinformatics, the 'parent' disciplines have different value systems; for example, what is considered worthwhile research by computer scientists can be thought of as trivial by biologists, and vice versa. This paper concentrates on the problems of reward and recognition described by scientists working in academic bioinformatics in the United Kingdom. We highlight problems that are a consequence of its cross-cultural make-up, recognising that the mismatches in knowledge in this borderland take place not just at the level of the practical, theoretical, or epistemological, but also at the cultural level too. The trend in big, interdisciplinary science is towards multiple authors on a single paper; in bioinformatics this has created hybrid or fractional scientists who find they are being positioned not just in-between established disciplines but also in-between as middle authors or, worse still, left off papers altogether

Cellular Islet Autoimmunity Associates with Clinical Outcome of Islet Cell Transplantation

Islet cell transplantation can cure type 1 diabetes (T1D), but only a minority of recipients remains insulin-independent in the following years. We tested the hypothesis that allograft rejection and recurrent autoimmunity contribute to this progressive loss of islet allograft function.Twenty-one T1D patients received cultured islet cell grafts prepared from multiple donors and transplanted under anti-thymocyte globulin (ATG) induction and tacrolimus plus mycophenolate mofetil (MMF) maintenance immunosuppression. Immunity against auto- and alloantigens was measured before and during one year after transplantation. Cellular auto- and alloreactivity was assessed by lymphocyte stimulation tests against autoantigens and cytotoxic T lymphocyte precursor assays, respectively. Humoral reactivity was measured by auto- and alloantibodies. Clinical outcome parameters--including time until insulin independence, insulin independence at one year, and C-peptide levels over one year--remained blinded until their correlation with immunological parameters. All patients showed significant improvement of metabolic control and 13 out of 21 became insulin-independent. Multivariate analyses showed that presence of cellular autoimmunity before and after transplantation is associated with delayed insulin-independence (p = 0.001 and p = 0.01, respectively) and lower circulating C-peptide levels during the first year after transplantation (p = 0.002 and p = 0.02, respectively). Seven out of eight patients without pre-existent T-cell autoreactivity became insulin-independent, versus none of the four patients reactive to both islet autoantigens GAD and IA-2 before transplantation. Autoantibody levels and cellular alloreactivity had no significant association with outcome.In this cohort study, cellular islet-specific autoimmunity associates with clinical outcome of islet cell transplantation under ATG-tacrolimus-MMF immunosuppression. Tailored immunotherapy targeting cellular islet autoreactivity may be required. Monitoring cellular immune reactivity can be useful to identify factors influencing graft survival and to assess efficacy of immunosuppression.Clinicaltrials.gov NCT00623610

Organization, Evolution, Cognition and Dynamic Capabilities

Using insights from ‘embodied cognition’ and a resulting ‘cognitive theory of the firm’, I aim to contribute to the further development of evolutionary theory of organizations, in the specification of organizations as ‘interactors’ that carry organizational competencies as ‘replicators’, within industries as ‘populations’. Especially, I analyze how, if at all, ‘dynamic capabilities’ can be fitted into evolutionary theory. I propose that the prime purpose of an organization is to serve as a cognitive ‘focusing device’. Here, cognition has a wide meaning, including perception, interpretation, sense making, and value judgements. I analyse how this yields organizations as cohesive wholes, and differences within and between industries. I propose the following sources of variation: replication in communication, novel combinations of existing knowledge, and a path of discovery by which exploitation leads to exploration. These yield a proposal for dynamic capabilities. I discuss in what sense, and to what extent these sources of variation are ‘blind’, as postulated in evolutionary theory.

Patient and caregiver priorities for medication adherence in gout, osteoporosis and rheumatoid arthritis: nominal group technique

Objectives: This study aimed to identify and prioritize factors important to patients and caregivers with regard to medication adherence in gout, osteoporosis (OP) and rheumatoid arthritis (RA), and to describe the reasons for their decisions. Methods: Patients with gout, OP and RA, and their caregivers purposively sampled from five rheumatology clinics in Australia, identified and ranked factors considered important for medication adherence using nominal group technique and discussed their decisions. An importance score (scale 0-1) was calculated, and qualitative data were analysed thematically. Results: From 14 focus groups, 82 participants (67 patients, 15 caregivers) identified 49 factors. The top five factors based on the ranking of all participants were trust in doctor (importance score 0.46), medication effectiveness (0.31), doctor's knowledge (0.25), side effects (0.23), medication taking routine (0.13). The order of the ranking varied by participant groupings with patients ranking trust in doctor the highest whilst caregivers ranked side effects the highest. Five themes reflecting the reasons for factors influencing adherence were: motivation and certainty in supportive individualised care; living well and restoring function; fear of toxicity and cumulative harm; seeking control and involvement; and unnecessarily difficult and inaccessible. Conclusions: Factors related to the doctor, medication properties and patients' medication knowledge and routine were important for adherence. Strengthening doctor-patient trust and partnership, managing side effects, and empowering patients with knowledge and skills for medicine-taking could enhance medication adherence in patients with rheumatic conditions